PTL 1 discloses a compound having a Griffin's HLB value of 10 to 16 and represented by the following General Formula (1): CnF2n+1—CH2CH(OH)CH2O—(CH2CH2O)a—Y (1), where n is an integer of 2 to 6, a is an integer of 15 to 50, Y represents —CbH2b+1 (b is an integer of 11 to 19) or —CH2CH(OH)CH2—CmF2m+1 (m is an integer of 2 to 6). PTL 1 also discloses that the above compound serves as a surfactant, and can be used in aqueous paint compositions, aqueous ink compositions and photosensitive photographic materials. However, there is a concern that this compound may decrease surface tension when used even in small amounts. Also, the compound has a disadvantage in that, once foam has been generated, the foam does not disappear altogether.
PTL 2 discloses a composition containing N-methyl-2-pyrrolidone (NMP) which is for cleaning nozzles of inkjet printers. However, since the surfactant properties of NMP are low, it is inferior in paper permeability as well as wetability with respect to the interior flowpath of liquid jetting devices.
PTL 3 discloses a filling liquid for ink supplying systems which is supplied to inkjet apparatuses and contains a fluorine-containing surfactant and an organic solvent having a boiling point of 150° C. or higher. In PTL 3, a perfluoroalkyl ethylene oxide additive is exemplified as the fluorine-containing surfactant, and an N-methyl-2-pyrrolidone is exemplified as the organic solvent.
While these fluorine-containing surfactant and organic solvent are used in the filling liquid for ink supplying systems, PTL 3 does not suggest use of them as a treatment liquid for inkjet apparatuses.
Also, in general, fluorine-containing surfactants have a disadvantage in that, once foam has been generated, it is difficult to eliminate the foam. Thus, variations in coating arise due to air bubbles.
One feature required for a liquid jetting device treatment liquid is the abilities to be appropriately wettable to media and to be uniformly jetted or coated thereonto. By allowing the treatment liquid to have appropriate wetability, it is possible to improve the penetration speed at which the treatment liquid penetrates media, and it becomes possible to improve ablation resistance and overcome such problems as bleeding. In particular, permeability of a treatment liquid with respect to media is of great importance. If such permeability is low, a large amount of the treatment liquid will remain in the vicinity of the medium surface. As a result, when the treatment liquid comes into contact with a colorant-containing second jetting liquid on the medium surface, the acid or multivalent metal salts in the treatment liquid and the carboxyl group-containing resin (enveloping the colorant) in the second jetting liquid start an excessive aggregation reaction, which leads to insufficient embedding of the solid image due to reduction in dot diameter. There is also a problem with ablation resistance due to an excessive amount of colorant components remaining on the medium surface.
Adding a surfactant to reduce surface tension and thereby improve wetability of the treatment liquid is generally performed. Among others, fluoroalkyl group-containing surfactants are known to have an ability to considerably reduce the surface tension when solved in water, and are thus widely used in liquids for liquid jetting devices. However, the aspect of having high surfactant ability means that micelle is easily formed between surfactants, which as a result, leads to a disadvantage of foam being formed easily.
Many problems in the system will follow once foam is formed. For example, air bubbles are generated in the subtank as a result of vibration of liquid during printing operation in movable-head type printers, and will lead to problems with rising of the ink level within the subtank which can cause erroneous ink level gauging. And when bubbles are mixed into the treatment liquid during application of the treatment liquid onto media, coating variation will occur, leading to problems in variation in image density.
In order to solve this problem of foam generation, there is a generally known method of forcefully eliminating generated foam bubbles by adding a silicone-based defoamant as described in Japanese Patent Application Laid-Open (JP-A) No. 2009-001741. The mechanism of the foam bubble elimination is that foam bubbles are eliminated when the defoamant penetrates the bubble lamellar film and scatters thereby replacing surfactant with defoamant. For this to occur, the defoamant must be non-compatible with the system. In general, a hydrophobic silica or polyurea is added to a water-based defoamant as an active ingredient, and though it is hydrophobic and thus will exist in a state dispersed as particles which do not solve in the system, it can cause filter clogging and thus, preferably, no defoamant is used.
As described above, since wetability and foam generation go hand in hand, it has been difficult to satisfy both without problems.